Transient Bleaching of the F‐Band in Alkali Halides

Dokter, G.; Hoffmann, Hans‐Jürgen

doi:10.1002/pssb.2220760125

Cited by 9 publications

(2 citation statements)

References 22 publications

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“…1, this additional recombination is assumed to occur directly from the conduction band into the ground state (process V). This assumption is supported by the fact that the activation energies of F & and of the corresponding time constant 6 are equal within the limits of the experimental error [15], whereas according to the kinetics with precapture into F* both activation energies should differ by E (compare equations (17) and (20)). Whether this additional recombination is radiative or radiationless can be evidenced directly by measurements of the F-center luminescence quantum yield in the steady state as a function of the temperature.…”

Section: Comparison With Former Resultsmentioning

confidence: 91%

Recombination kinetics of electrons with α‐ centers in colored alkali halides

Hoffmann¹

1981

Physica Status Solidi (b)

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The recombination kinetics of conduction electrons with halogen-ion vacancies (a-centers) in additively colored alkali halides is calculated and discussed for the high-temperature range, in which concurring F'-centers decay thermally. The steady state concentrations of conduction electrons, a-, andF'-centers as well as the time constants are explicitly given under the assumption that the charge carriers recombine with a-centers predominantly via the excited state F * of the vacancies. These results are compared with experimental data and former theoretical calculations for the case that recombination directly into the ground state is predominant. The results on the effective recombination coefficient can also be applied to other defects in photoconductors and semiconductors if the charge carriers recombine via an excited state.Die Kinetik der Rekombinat ion von Leitungselektronen mit Halogenionlucken (a-Zentren) in additiv verfarbten Alkalihalogeniden wird fur den Temperaturbereich berechnet und diskutiert, in dem F-Zentren thermisch instabil sind. Es werden sowohl die stationaren Konzentrationen von Leitungselektronen, a-und F'-Zentren als auch die zugehorigen Zeitkonstanten explizit angegeben unter der Annahme, dal3 die Ladungstrager mit den a-Zentren iiberwiegend iiber den angeregten Zustand F * rekombinieren. Diese Ergebnisse werden mit experimentellen Daten und fruheren Rechnungen, bei denen ausschliel3lich direkte Rekombination in den Grundzustand angenommen wurde, verglichen. Die Ergebnisse fur den effektiven Rekombinationskoeffizienten konnen auch auf andere Storstellen in Photound Halbleitern angewendet werden, sofern die Rekombination dort iiber einen angeregten Zustand erfolgt.

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Section: Comparison With Former Resultsmentioning

confidence: 91%

Recombination kinetics of electrons with α‐ centers in colored alkali halides

Hoffmann¹

1981

Physica Status Solidi (b)

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“…The rate equations of the reaction kinetics described have been established and discussed as a function of temperature, photon flux density and Fcentre concentration [61]. The theoretical results have been tested and verified by experiments of both the photoconductivity of the electrons in the conduction band and photochromy due to the induced absorption band of the F ' -centres as a function of time using rectangular photon pulses [62,63].…”

Section: Photo Induced Reactions Of Colour Centres In Alkali Halidesmentioning

confidence: 99%

Transitions of electrons and holes drive diffusion in crystals, glasses and melts

Hoffmann

2020

Materialwissenschaft Werkst

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Diffusion of atoms or molecules (generally: particles) is driven by differences and gradients of the chemical potential of the particles in their accessible space. If the difference of the chemical potential is due to differences of concentrations alone, one arrives at the diffusion equations of Fick. The diffusion coefficients are described in known models by vibrations of atoms in condensed matter which cause the exchange of preferentially neutral particles with neighbouring particles, impurities, interstitial places and vacancies near or on surfaces, grain boundaries, dislocation lines and in the homogeneous bulk. The rates of electronic transitions, however, increase also in melts and solids of chemically bonded particles with increasing temperature. Such transitions cause large fluctuating deviations of the local energy, the charge distribution and the local chemical and electrical potentials. The fluctuating deviations interact with the core ions and drive particles to interchange. This mechanism that supplements the known mechanisms of diffusion has not yet found adequate attention in the literature until now. Foundations, experimental results, evidence and consequences for diffusion are discussed.

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To what extent are the observed lifetimes of F‐centers intrinsic?

Bosi

Nimis²

1979

Physica Status Solidi (b)

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(a, b) and M. NIMIS (a) New measurements, performed a t near 65 K, of the F-center radiative lifetime tR in KBr samples containing a-and F'-centers show a tK-increase which is related t o low and, in some cases, scarcely detectable, critical oc-center concentrations. Analysis of experiments known in literature reveals that a far from negligible quantity of a-centers is always present in real crystals. These facts lead us to the stimulating hypothesis that the tR-values might be incorrect because of the perturbation due to the interaction between F-and &-centers.Neue Messungen bei ungefahr 65 K zeigen eine Zunahme der Strahlungslebensdauer des F-Zentrums in KBr-Kristallen, die a-und F'-Zentren enthalten. Diese Zunahme ist mit einer kritischen Konzentration yon oc-Zentren verbunden, die meistens sehr klein und in manchen Fallen schwerlich meBbar ist. Aus einer Analyse der verschiedenen experimentellen Ergebnisse, die in der Literatur beschrieben sind, geht deutlich hervor, daB in Realkristallen immer eine nicht unbedeutende Menge von a-Zentren vorhanden ist. Diese Tatsachen fuhren zu der provoziereiiden Annahme, da[3 die bekannten tn-Werte, infolge der Wechselwirkung zwischen F-und oc-Zentren nicht genau smd.

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Transient Bleaching of the F‐Band in Alkali Halides

Cited by 9 publications

References 22 publications

Recombination kinetics of electrons with α‐ centers in colored alkali halides

Recombination kinetics of electrons with α‐ centers in colored alkali halides

Transitions of electrons and holes drive diffusion in crystals, glasses and melts

To what extent are the observed lifetimes of F‐centers intrinsic?

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